It feels more like a bug to me. The existing code throws a parsing exception when I fetch the bodystructure of the message in my inbox that prompted me to make this change. I have not dug deep enough into the RFCs yet to know how close this is or is not to the IMAP specs (to the best of my knowledge, this is not coming from any sort of new IMAP extension, though I do not discount that this could potentially be a bug in Google's IMAP implementation), and I know this is not the first delivery status notification email to have a problem with Net::IMAP.